It is possible to write (22) in a tensor form as in [1]}
\(\frac{\partial (\rho v_{i})}{\partial t}+\frac{\partial (\rho u_{i}v_{j})}{\partial x_{j}}=-\frac{\rho }{m} \frac{\partial V}{\partial x_{i}}-\frac{\partial \sigma _{ij}}{\partial x_{j}}-\frac{2\varepsilon }{m\hbar }\rho Q v_{i},\) 
